The concept of forming subterranean wells is referred to; a drill string is typically used to drill a wellbore of a first depth into the formation.
While drilling, a drilling fluid (ormud fluid) is circulated down through the tubular string, then through perforation(s) in a drill bit which is located at the end of the drill string. Then, the drilling fluid continues the circulation up through the annular flow passage between the outer perimeter of the tubular string and inner wall of the well.
The mud jets from the bit nozzles are normally directed toward the hole bottom and formation being drilled, with the velocities of several hundred feet per second to create turbulence which serves to clean the bit, as well as carry away the cut chips. The drill bit nozzles are removable flow-restrictors which determine the total area of the drill bit outlet, and therefore the terminal velocity of the mud jet.
The majority of drilling systems in current use include a heavy tubular string with a substantially large outer diameter, and a Bottom Hole Assembly (BHA) linked to that tubular string and located below it. The BHA may include the drill bit, as well as other equipment such as motors, logging while drilling equipment, directional drilling control systems, or any combination thereof. Above the BHA, there normally extend smaller drill pipes connecting the BHA to the surface.
When drilling in earth formations having rapid variations in mechanical properties between layers, the drill bit nozzle hydraulic horse power per square inch (HSI) can be too high for the formation, resulting in the formation being overdrilled, or can be too low for the formation, which results in less efficient removal of cuttings.
Conventionally, the drill bit nozzle lowered in the wellbore has a fixed flow geometry and total flow area (TFA). It is not possible to change to another nozzle geometry except through pulling the tubular string out of the wellbore.
Flow restrictors used within a tubular string during drilling, for example for the mud motor, may have a fixed geometry connecting between the inner flow passage and the annular flow passage. It is desirable to be able to change the flow restrictor flow geometry without the need to pull the tubular string out of the hole.
Flow restrictors exist in other components of the tubular string used for drilling or conduits used for flow of fluid in certain industries (like the oil and gas industry, or other industries at large) that communicate fluid from one point to another. Changing the geometry of flow restrictors remotely is desirable.
The majority of drilling systems used today use drill bit nozzles with fixed total flow area (TFA). One way to change the drill bit nozzle HSI is to change the mud flow rate through the whole drilling string, i.e. reduce mud circulation flow rate or increase the flow rate from the optimum flow rate.
Another way to change nozzle Total Flow Area (TFA) of the drill bit or other flow restrictor disposed within the conduit is to pull out the tubular string from the wellbore and replace the nozzle with another of the desired TFA.
A previously-described adjustable geometry nozzle requires the operator to pull the string out of the wellbore.
Changing mud flow rate from the optimum to adjust the HSI requires reducing mud circulation flow rate or increasing the flow rate from the optimum flow rate. This results in undesired annular flow velocity which causes deterioration in the hole cleaning efficiency through increase of suspended solids or cuttings within the wellbore or causing a washout when formation or other undesirable acts.
Pulling out the tubular string from the wellbore to replace the nozzle with another of the desired TFA cost the operator significant time and money and increase drilling risks.
One aspect of the current invention is to introduce methods and apparatus to remotely change the geometry of a drill bit nozzle which allows to adjust the HSI of the nozzle while maintaining optimum flow rate. Another aspect of the present invention is to introduce an apparatus and method for remotely and selectively changing flow profile within the tubular string or between the tubular string inner flow passage and annular flowpassage.
Maintenance of annular velocity and the introduction of adjustable TFA drill bit nozzles using the current invention will reduce the operating cost and risks associated with suspended solids or cuttings as well as risks associated with possible formation collapse.
Drill bit nozzles are made of fixed size, therefore drill bit manufacturers provide different drill bit designs with alternative number of nozzles and sizes. A typical nozzle (shown in FIG. 3) is inserted into an aperture, and is held in place by any one of several means, such as a snap ring, screw threads, or a nail lock. The inner diameter of the nozzle outlet is approximately equal to the opening above which. The final outlet internal diameter of the nozzle is measured in increments of 1/32 of an inch. To adjust the flow, the nozzle has to be replaced with another nozzle which has a different outlet inner diameter.
Replacing a drill bit nozzle requires pulling the drill string out of the hole (POH) which retards drilling operation and multiplies drilling cost. The size of nozzle needed cannot be determined in advance due to the many factors affecting nozzle sizing. Therefore, drill bits are commonly shipped off-shore with several nozzles with different sizes for each aperture. At the drilling site, the correct-size nozzle is installed whereas unused nozzles are normally discarded or lost which increases the cost and time of drilling.
In a more recently disclosed invention, a drill bit nozzle with adjustable orifice is proposed (shown in FIG. 4A). This design allows the same nozzle to deliver the mud at variable pressures. This is accomplished by the use of two thick plates, each having a shaped aperture therein. The degree to which the two apertures are overlapped determines the size of the orifice. The movement of at least one of the plates, and thus the size of the orifice, can be adjusted at the drill site, to give a desired pressure drop across the nozzle.